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Lamprey, fishermen not off hook yet
Dioxin role unclear in all Great Lakes
By Susanne Quick
Milwaukee Journal Sentinel

While researchers and fisheries managers across the Great Lakes region have mostly lauded the study as well-executed, thorough and comprehensive, they believe the situation is murky outside the confines of the small, most easterly lake in the chain.

And they're reluctant to let commercial fishermen and the exotic sea lamprey off the hook quite yet.

A recent study by a team of researchers from federal agencies and North American universities demonstrated that lake trout probably weren't done in by the double-edged sword of lamprey and commercial fishing in Lake Ontario - the conventional scenario of this once plentiful fish's demise there.

Instead, they say, populations of this top predator were whittled away as toxic byproducts from combustion and industrial activities, called dioxins, seeped into the waters and soils of Lake Ontario - effectively preventing fertilized eggs from hatching.

"I have to say I was really jazzed when I saw this" study, said Mike Staggs, director of fisheries at the Wisconsin Department of Natural Resources. "It provides a piece" of the lake trout puzzle in the Great Lakes.

But he and other fishery managers across the region remain circumspect about its meaning elsewhere.

Complicating the situation, it appears that nobody has data on the dioxin levels in the sediments of lakes other than Lake Ontario - except for Philip Cook, the primary researcher of the Lake Ontario study and a research chemist at the U.S. Environmental Protection Agency.

He has samples of eggs, tissue and sediment from Lake Michigan in his freezer but has not published his results, and therefore was reluctant to release the numbers.

Queries to state agencies revealed that samples of these sorts for the most part have not been collected. And if they have been, they are incomplete.

So, the question of whether dioxins played a role in the history of lake trout relies on circumstantial and correlative data based on historical records of lake trout numbers, commercial catches and lamprey estimates.

And using this data, everybody - fish biologists and toxicologists - agrees that at least one lake was immune to any chemical effect.

The lake trout population in Lake Superior, which holds nearly 3,000 cubic miles of water and has relatively few potential dioxin producers on its shores, was unlikely to have succumbed to the chemical culprit. Here, the lake trout die-off was most likely the result of excessive commercial fishing and lamprey.

Indeed, subsequent lake trout management on Lake Superior supports this observation. The closing of commercial fishing in 1961 and programs designed to actively reduce lamprey populations brought back lake trout numbers to near historical highs, concluded Mike Hansen, a fisheries biologist and professor of fisheries at the University of Wisconsin-Stevens Point, in a paper in the Journal of Great Lakes Research in 1995.

Guessing game

However, the same can't be said for Lake Michigan, where similar measures have been taken to bring back lake trout. And this is where the dioxin puzzle-piece may fit in, said Staggs. Although, he acknowledges that debate resounds on this score, too.

For instance, while Hansen agrees that "Lake Michigan would seem to be the most likely lake where similar levels of contamination" to Lake Ontario may have been present, he cited a 2002 study from another group of federal and university researchers, who "found no basis for invoking contamination in the demise of lake trout or the continued failure of lake trout to reproduce."

"Most people want to believe that contaminants cause(d) problems with fish reproduction, so any evidence that suggests such a linkage is quite appealing," he said in an e-mail, qualifying his statement by saying that he had not read the Lake Ontario paper thoroughly, nor is he a lower Great Lakes specialist.

But, he "can find no one in the fishery community who actually believes that contaminants were implicated in the demise of any fish population in the Great Lakes, though some contaminant experts continue to beat the drum."

Levels in water are low

Mike Hammers, a wastewater engineer with the DNR, is dubious, too.

Wisconsin paper mills release minute amounts of dioxin into Wisconsin lakes and rivers, he said, but they fall far below the numbers cited in the Lake Ontario study.

"We're talking 3 parts per quintillion," - a millionth the amount of the Lake Ontario numbers, he said.

"I can't tell you what was there in the past," Hammers said, but the levels now found in the water column - near areas where discharge from paper mills and factories enters the environment - are much smaller than the amounts thought to cause problems.

But to Cook, the lead researcher on the Lake Ontario study, comparing water column numbers with sediment and egg analyses is like comparing apples and watermelons. And although formulas have been devised to compare the two, the real test is to look at the content in the eggs - a task he is working on.

The bottom line, he said, is that no one knows the minimum levels of dioxin that affect lake trout. So although low levels might not necessarily kill developing eggs - as was seen in the Lake Ontario study - there might be other harmful side effects.

These low-level effects, called sub-lethal effects, are believed to cause problems ranging from neurological and cardiac deficiencies to blindness. And the effects on the reproduction - and viability - of adult fish remains a question, Cook said.

"Their vulnerability may be greater than what we have documented," he said. "We just don't know at this point."

Studies on rainbow trout, using chemical cocktails that mimic the levels, profiles and configurations of Lake Michigan dioxins, have shown sub-lethal effects such as delayed hatch timing, mild hemorrhaging and swelling of the yolk sac, said Richard Peterson, a toxicologist at UW-Madison, and one of the authors on the Lake Ontario paper.

But "we still have a big information gap" on sub-lethal effects, he said.

Yet, both he and Cook are concerned because lake trout appear to be more sensitive to dioxins than other fish.

Why this is so is not known, said Peterson. "That's the million-dollar question."

Maybe, said Roger Bergstedt, a research fishery biologist with the U.S. Geological Survey who was not involved in the study. But as far as he is concerned, the search for what happened to lake trout is irrelevant.

"Current management requires that we try to keep lamprey populations down," he said. If we let them be, they'll come back in force.

He cited work he had done on Lake Erie, where a four- or five-year hiatus in treating streams for lamprey created a boom in the blood-sucking critters.

"Mortality rates of lake trout became unacceptable," he said.

The point now, he said, is to manage what we have.

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